In the unwinding of webs of flexible material, e.g. paper or paperboard, it is frequently desirable upon replacement of the wound roll or the substitution in the machine of a new fully-wound roll for a roll which has been unwound, to splice the trailing portion of a previously unwound web with a leading portion of the web unwound from the new roll. It is desirable that the splicing be carried out at full unwinding speed, i.e. without braking or stopping the trailing portion of the web and also to effect the splicing in a butt junction, i.e. without overlapping the trailing portion of the web with the leading portion of the new web. The advantage of a butt connection over an overlap connection is that unnecessary thickening of the web can be obviated, such thickening creating problems in many cases in the subsequent operations with the web. The subsequent operations to which the web may be subjected after unwinding can include, for example, coating.
In order to form a butt connection without slowing the speed of the web during the unwinding process, German patent document DE-OS 23 03 856 describes a splicing unit in which the trailing portion of the web previously unwound from a roll is passed together with the leading portion of the new web about a grooved roller and the webs are cut on the grooved roller by the blade of a blade roller resting against the grooved roller. After the cut residue of the trailing web is separated from the leading portion of the new web, an adhesive strip is applied to connect the newly-formed leading edge of the new web with the newly-formed trailing end of the previously unwound web. The adhesive strip can be laid into a groove in the blade roller before the beginning of the splicing operation and can be transferred to the webs from this groove.
To guide the leading end of the new web through the splicing unit, a separate winding roller engages the leading end of the web from the new roll and passes it through the gap between the grooved roller and the winding roller, whereby the new web is wound in an intermediate winding on the winding roller. To separate the two webs, i.e. sever them in the manner described, the groove roller is moved against the blade roller. The material from the leading end which remains wound on the winding roller is treated as lost material and is ultimately removed from the winding roller.
Prior art unwinding apparatus was characterized by complex mechanisms and high materials loss.